A known cooling storage cabinet is described in Patent Document 1. In this art, a freezing compartment and a refrigerating compartment are formed by separating the inside of a heat-insulating storage cabinet body. The freezing compartment and the refrigerating compartment each are heat insulated. The freezing compartment and the refrigerating compartment each have respective set temperatures differing from each other. Each of the compartments has an evaporator, and a single compressor supplies refrigerant alternately to evaporators to cool the compartments.
More specifically, a cooling cycle is configured as follows. An inverter motor operates a compressor. An outlet side of the compressor is connected to a condenser. The downstream side of the condenser is branched in two refrigerant supply paths through a three-way valve. A capillary tube and one of the evaporators are installed in each of the refrigerant supply paths. Outlets of the evaporators each have a common connection and have a supply path back to the compressor. During operation of the compressor, refrigerant is supplied alternately to the two evaporators by switch of the three-way valve, whereby the freezing compartment and the refrigerating compartment are alternately cooled. In a case where the internal temperature of either one of the freezing compartment and the refrigerating compartment is lower than the set temperature, the other compartment is individually cooled. In a case where the internal temperatures of both of the freezing compartment and the refrigerating compartment are lower than the set temperatures, the compressor is stopped.
On the other hand, in the case where the compressor is operated by the inverter motor, it is proposed in some arts to cool each of the compartments along a predetermined temperature curve. For example, a target temperature curve is stored in advance, and then rotational speed of the compressor is controlled in response to a deviation between a target temperature and an actual internal temperature, and thereby the compartment is maintained at the target temperature. With this control method, a continuous ON time of the compressor can be longer. In other words, the number of switching between ON and OFF is significantly decreased. Thus, higher performance and energy consumption can be realized.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2001-133113
Meanwhile, in the case of performing the control of the compressor as above, when cooling load is higher because of a circumstance such as a higher ambient temperature, the rotational speed of the compressor tends to be controlled at a higher speed. When the alternate cooling of the freezing compartment and the refrigerating compartment as shown in FIG. 12 is performed under such conditions and when the internal temperature of the freezing compartment becomes lower than the set temperature i.e. a temperature TF(off), the individual cooling of the refrigerating compartment is started. However, because of such a higher rotational speed of the compressor, there is a concern of over cooling capacity, which results in over cooling of the refrigerating compartment.
Here, in line with conditions of actual use, supposing a case where stored objects are placed on net racks 2 in the refrigerating compartment 1, faces of the net racks 2 are covered with plates 3 as shown in FIG. 13. Then, the temperature (a temperature curve y shown by dashed line in FIG. 12) at a point 5 above an uppermost net rack 2, which is in front of a cold air outlet from an internal fan 4, is rather lower than the temperature (a temperature curve x shown by solid line in the same figure) in the vicinity of an internal air inlet, where a R-compartment temperature sensor 6 is positioned. Admittedly, when the temperature detected by the R-compartment temperature sensor 6 becomes lower than the set temperature, i.e. reaches a temperature TR(off), the cold air stops blowing out. However, until that moment, the difference in temperature distribution may cause an over-cooled local zone such as the zone on the uppermost net rack 2. This is a problem.
The present invention was completed based on the circumstances as above, and it purpose is to prevent overcooling of the storage compartment in the case of switching from the alternate cooling of the plurality of storage compartments having different set temperatures to the individual cooling of the storage compartment having higher set temperature.